Fabrication and properties of Cf/ZrC‐SiC‐based composites by an improved reactive melt infiltration

C_f/ZrC‐SiC composites with a density of 2.52 g/cm³ and a porosity of 1.68% were fabricated via reactive melt infiltration (RMI) of Si into nano‐porous C_f/ZrC‐C preforms. The nano‐porous C_f/ZrC‐C preforms were prepared through a colloid process, with a ZrC “protective coating” formed surrounding the carbon fibers. Consequently, highly dense C_f/ZrC‐SiC composites without evident fiber/interphase degradation were obtained. Moreover, abundant needle‐shaped ZrSi₂ grains were formed in the composites. Benefiting from this unique microstructure, flexural strength, and elastic modulus of the composites are as high as 380 MPa and 61 GPa, respectively, which are much higher than C_f/ZrC‐SiC composites prepared by conventional RMI.     

催化剂结构与焦油模型化合物裂解行为的关联性

以Ni（NO₃）₂·6H₂O为镍源,分别以HZSM-5（Si/Al=25）、HZSM-5（Si/Al=50）、HZSM-5（Si/Al=200）、USY、Al₂O₃为载体制备了5种镍基催化剂,采用XRD、H₂-TPR、BET、NH₃-TPD等方法对其进行了表征,在固定床反应器中考察了上述催化剂对煤焦油模型化合物甲苯+芘的催化裂解性能。结果表明,相比惰性载体石英砂,在催化剂作用下,液相产物中轻质芳烃种类明显增多。3种Ni/HZSM-5催化剂的比表面积和平均孔径较为接近,然而酸性中心数量最多的Ni/HZSM-5（Si/Al=25）,对甲苯+芘的裂解能力最强,体现为液体产物收率最低（仅为15.95%）,气产率和析碳率均最高,分别达16.73%和67.32%。在酸性中心数量相近的Ni/HZSM-5（Si/Al=200）与Ni/Al₂O₃作用下,液体产物收率差别较小,但后者的芘裂解率比前者高41.47%,主要是由于后者的平均孔径比前者高1.64倍,说明平均孔径大有利于重质组分芘的裂解。综合考虑液体产物收率、气产率、析碳率和芘的裂解率,Ni/Al₂O₃更适合甲苯+芘裂解反应体系。     

Influence of Yb Concentration on the Optical Properties of CaF2 Transparent Ceramics Codoped with Er and Yb

Er, Yb:CaF₂ nanoparticles with different Yb concentrations were synthesized by a coprecipitation method using nitrates as raw materials. X‐ray powder diffraction and transmission electron microscopy analysis showed that the nanoparticles were single fluorite phase and the nanoparticle size was found to decrease with increasing Yb concentrations. The obtained nanoparticles were hot‐pressed at 800°C under 30 MPa under vacuum environment to fabricate Er, Yb:CaF₂ transparent ceramics. The influence of Yb ion concentrations on the optical transmission, microstructure, and luminescence properties of Er, Yb:CaF₂ transparent ceramics were investigated. The addition of Yb ions was found effectively to reduce grain size and has a positive effect on improving the optical transmission of Er, Yb:CaF₂ transparent ceramics. The highest transmittance in the near‐infrared spectral region of the Er, Yb:CaF₂ transparent ceramic reached about 90%. The green, red, and near‐infrared emission intensities were found to increase with increasing Yb concentration.     

共混工艺对TPU/PVA共混物力学性能的影响

利用哈克密炼机,通过熔融共混法,制备了热塑性聚酯型聚氨酯(TPU)/聚乙烯醇(PVA)(质量比80/20)共混材料。探讨了工艺条件(温度、转速、加工时间)对TPU/PVA共混材料的扭矩、断裂伸长率、拉断永久变形和拉伸强度等力学性能的影响。结果表明,最佳加工条件为:加工温度170℃,转速60 r/min,加工时间8 min。     

Effects of surface modification of self‐healing poly(melamine‐urea‐formaldehyde) microcapsules on the properties of unsaturated polyester composites

Poly(melamine‐urea‐formaldehyde) (MUF) microcapsules used as self‐healing component of composites were prepared by in situ polymerization. The surface of MUF microcapsules was modified by 3‐aminopropyltriethoxy silane‐coupling agent (KH550). The interfacial interactions between MUF microcapsules and KH550 were studied by Fourier transform infrared spectra (FTIR). FTIR results show that the silane‐coupling agent molecule binds strongly to the MUF microcapsules surface. A chemical bond (Si? O? C) is formed by the reaction between the Si? OH and the hydroxyl group of MUF microcapsule. This modification improves the thermal properties of microcapsules. Optical microscope (OM) and scanning electron microscope (SEM) show that a thin layer is formed on the surface of MUF microcapsules. The interfacial adhesion effect between MUF microcapsules and unsaturated polyester matrix was investigated. MUF microcapsules disperse evenly in the composites. When crack propagated, the microcapsules were broken and the repair agent flowed from the microcapsules to react with the curing agent. Then the crosslinking structure was formed and the composite was repaired. The tensile properties, impact properties, and dynamic mechanical properties of composites have been evaluated. The results indicate that the silane‐coupling agent plays an important role in improving the interfacial performance between the microcapsules and the matrix, as well as the mechanical properties of the composites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Mechanistic insights into the structure‐dependent selectivity of catalytic furfural conversion on platinum catalysts

The effects of surface structures on the selectivity of catalytic furfural conversion over platinum (Pt) catalysts in the presence of hydrogen have been studied using first principles density functional theory (DFT) calculations and microkinetic modeling. Three Pt model surface structures, that is, flat Pt(111), stepped Pt(211), and Pt₅₅ cluster are chosen to represent the terrace, step, and corner sites of Pt nanoparticle. DFT results show that the dominant reaction route (hydrogenation or decarbonylation) in furfural conversion depends strongly on the structures (or reactive sites). Using the size‐dependent site distribution rule, our microkinetic modeling results indicate the decarbonylation route prevails over smaller Pt particles less than 1.4 nm while the hydrogenation is the dominant reaction route over larger Pt catalyst particles at T = 473 K and = 93 kPa. This is in good agreement with the reported experimental observations. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3812–3824, 2015     

Preparation and characterization of P(AN‐co‐VA‐co‐DEMA) fibers coated with multiwalled carbon nanotubes by electrostatic interactions

P(AN‐co‐VA‐co‐DEMA) terpolymers were synthesized by aqueous precipitation copolymerization of acrylonitrile (AN), vinyl acetate (VA), and 2‐dimethylamino ethyl methacrylate (DEMA) with an Na₂S₂O₅–NaClO₃ redox initiating system and fibers from these terpolymers were thus prepared by a wet spinning method. Functionalized multiwalled carbon nanotube (F‐MWNT) networks were created on the surface of P(AN‐co‐VA‐co‐DEMA) fibers by a simple dipping method. The morphology and interfacial interactions of the obtained F‐MWNTs‐coated fibers were characterized by scanning electron microscope, Raman spectroscopy, and Fourier transform infrared spectroscopy. The results showed that F‐MWNTs were assembled on the fibers and the density of F‐MWNTs can be controlled by adjusting the F‐MWNTs content in the dipping solution. The assembly process was driven by electrostatic interactions between the negative charges on the nanotube sidewalls and the positive charges of the fibers. The F‐MWNTs‐coated fibers had a good conductivity. The volume resistivity of the fibers coated with 1.18 wt % F‐MWNTs reached 0.27 Ω·cm, while the original mechanical properties were preserved. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42545.     

微波在橡胶工业中的应用

简述了微波加热的原理和特点,介绍了微波技术在国内橡胶工业中的应用,主要包括微波硫化、微波脱硫、微波干燥天然橡胶,最后对微波技术在橡胶加工中存在的问题和发展方向进行了展望。     

反硝化除磷脱氮理论及工艺研究进展

介绍了反硝化除磷脱氮的理论,并重点对几种比较典型的反硝化除磷脱氨工艺进行评述。     

流动注射电位法测定烟草中尼古丁的研究

以聚苯胺修饰的石墨管电极为基体电极,管内涂渍以硅钨酸为活性物质的聚氯乙烯（ＰＶＣ）膜,构成双膜流通式尼古丁电极,建立了流动注射电位法测定尼古丁的新方法,探讨了实验的最佳条件,用磷酸二氢钠－磷酸氢二钠缓冲溶液合并１．０×１０－５ｍｏｌ·Ｌ－１的尼古丁标准溶液作载液,对１．０×１０－４～１．０×１０－１ｍｏｌ·Ｌ－１的尼古丁溶液有良好线性响应,相关系数０．９９８５。本方法简便、选择性好,进样频率８０次·ｈ－１,适合大批量样品的快速测定,可用于检测烟草中的尼古丁。